JESS: Problem with adding a fact to the rete engine in Java

[Theunissen, Teun]

I am creating a fact in a java method. When I add this fact to the rete engine 
I get the following error:

An error occurred at line: -1
which look like: null
Errormessage: No slot __data in deftemplate  MAIN::answer


The problem is that the answer fact is an unordered fact and the deftemplate is 
defined in the MAIN module.
It seems that the rete engine handles this fact as an ordered fact.
What can I do to solve this problem?

The java code that builds the fact:

public void assertAnswer(String identifier, String answer, int valuetype)  {
  try {
    Fact afct = new Fact("answer", m_rete);

    afct.setSlotValue("ident", new Value(identifier,RU.SYMBOL));
    afct.setSlotValue("text", new Value(answer,valuetype));
    System.out.println(afct.toString());
    m_rete.assertFact(afct);

The messages on the console:

Focus: MAIN
(MAIN::answer (ident IL1_1) (text NEE))
JessEvent: [JessEvent: a fact was asserted]
An error occurred at line: -1
which look like: null
Errormessage: No slot __data in deftemplate  MAIN::answer

Kind regards
Teun Theunissen